If you are an International Medical Graduate, you are likely to apply to multiple specialties to have a safe margin. But have you considered these consequences- Do you have the personality for this specialty? Can you can be really happy in either specialty? Is one of them a back-up where you'll feel trapped and hopeless?
I hope you seriously consider these issues when you apply for Residency training. Waiting for one more match year may sound really painful, but it's better to take a year off and strengthen your credentials for the specialty of your dreams rather than commiting yourself to something you're not happy about. It makes more sense to apply to PGY-1 preliminary programs ( eg. prelim-surgery) if you have to think at all about back-up, because switching specialties is very difficult ( you will need a letter from your current program director, find an open slot, interview there while in PGY-1) and you don't want to burn bridges behind you when you leave your current program. Program Directors are not a bunch of ogres but they want you to come to their program happy and fulfilled.
The most popular combination seems to be IM and FM-I confess I am guilty to this offence :-) I am interested in primary care focused mainly towards adults, but broad enough to cover the extremes of age, and extra training in behavioral and psychosocial issues. I also liked the hours of outpatient practice better than inpatient practice- and FM programs usually has better focus on clinics in PGY-2 and PGY-3, as well as having "practice management" incorporated in the curriculum, which helps tremendously in learning to set up your own practice in the real world. Both IM and FM being primary care programs seemed to meet my goals, so in essence neither of them were back-up for me.
As I started digging further when applying, I actually found out that although it seemed like FM programs set their score filters lower (usually 85 or 80, sometimes no score filters but graduation year less than 2), the number of slots were only 4-5 per program. This means that if you get 2 interviews in an IM program with 30 slots, you may have a better chance of "matching" than interviewing at 6 FM programs with 4-5 slots! Also keep in mind that a lot of DOs also apply to Family Medicine as many DOs have strong interest in Sports Medicine. Since DOs are essentially schooled in the US and have formal US clinical experience, they may have an edge over IMGs. Also, a lot of Family Medicine programs are not even IMG-friendly. Even though it's a fact that most AMGs do not choose primary care programs, there are still many AMGs who go into Family Medicine for the lifestyle, family reasons, geographical flexibility, or pure interest. By the time most medical students apply to residency training, they are have a significant other, or are married with kids. This changes a lot of things in their career goals. Eg. In a metropolitan area where it's very desirable to live, with very good cultural activities, and job opportunities for the spouse, you'll find that FM programs are very, very hard to break into because of the stiff competition from AMGs.
That said, if you are applying to both FM and IM, make sure that in the CAF you mention ambiguous descriptions like "Medicine Wards/floors- 1 month externship" instead of using the words " Internal Medicine- 1 month externship". That way "IM" will not pop out when they screen the CAF to filter out people who look like 'fakes'. It really hurts a program's schedule when a PGY-1 switches to another program and they will do everything possible to screen them out early in the process. Plus, residents who come looking like they don't really want to be there come across very poorly with everyone and we all know how much "interpersonal skills" contribute to the evaluation of residents.
Also, FM interviews are very different from IM interviews and needs special preparation. In my opinion, interviews plays a more critical role in FM than in IM because of several factors, some of which I outlined above and mentioned in my previous entries. There will be a strong behavioral component to the interview with thorough analysis about the questions you ask, your percieved interest and knowledge about the specialty, your personality and suitability for the specialty, how "real" you look, etc.